Energy efficiency of lithium-ion batteries: Influential factors and long-term degradation

As the integration of renewable energy sources into the grid intensifies, the efficiency of Battery Energy Storage Systems (BESSs), particularly the energy efficiency of the ubiquitous lithium-ion batteries they employ, is becoming a pivotal factor for energy storage management. This study delves into the exploration of energy efficiency as a measure of a battery's adeptness in energy conversion, defined by the ratio of energy output to input during the discharge and charge cycles. Energy efficiency values were systematically calculated over the course of the battery lifespan, revealing a predominantly linear trend in the efficiency trajectories, as substantiated by the Mann–Kendall (MK) trend test. Subsequently, a linear model was proposed to represent the efficiency degradation. Further analysis shows that ambient temperature, discharge current, and cutoff voltage all affect energy efficiency in different ways. Using the energy efficiency and its behavior observed in this study, Battery Management Systems (BMS) can improve the energy efficiency of batteries by adjusting operating conditions or developing better management strategies.